Catálogo de publicaciones - libros

Quite unexpectedly, to many of us at least, Planck scale physics has in last years made irruption in present experimental physics. In these lectures I try to describe why this happened particularly in relation to Ultra High Energy Cosmic Ray Physics, and will discuss the potentialities of experiments in this field, in particular of the Pierre Auger Observatory. I will also present some (more theoretical) speculations.

It is not clear at all what is the problem in quantum gravity (cf. [3] or [8] for general reviews, written in the same spirit as the present one). The answers to the following questions are not known, and I believe it can do no harm to think about them before embarking in a more technical discussion.

After a brief review of the first phase of development of Quantum-Gravity Phenomenology, I argue that this research line is now ready to enter a more advanced phase: while at first it was legitimate to resort to heuristic orderof- magnitude estimates, which were suffcient to establish that sensitivity to Planck-scale effects can be achieved, we should now rely on detailed analyzes of some reference test theories. I illustrate this point in the specific example of studies of Planck-scale modifications of the energy/momentum dispersion relation, for which I consider two test theories. Both the photon-stability analyzes and the Crab-nebula synchrotron-radiation analyzes, which had raised high hopes of “beyond-Plankian” experimental bounds, turn out to be rather ineffective in constraining the two test theories. Examples of analyzes which can provide constraints of rather wide applicability are the so-called “time-of- fight analyzes”, in the context of observations of gamma-ray bursts, and the analyzes of the cosmic-ray spectrum near the GZK scale.

This article reviews many of the observational constraints on Lorentz symmetry violation (LV). We first describe the GZK cuto. and other phenomena that are sensitive to LV. After a brief historical sketch of research on LV, we discuss the effective field theory description of LV and related questions of principle, technical results, and observational constraints. We focus on constraints from high energy astrophysics on mass dimension five operators that contribute to LV electron and photon dispersion relations at order . We also briefly discuss constraints on renormalizable operators, and review the current and future constraints on LV at order ().

What is the fate of Lorentz symmetry at Planck scale? This question was the main theme of the Winter School and, as the reader could see from the proceedings, there are many possible answers. Here I would like to describe one possibility, whose central postulate is that in spite of the fact that departures from Special Relativity are introduced at scales close to Planck scale, one keeps unchanged the central physical message of the theory of relativity, namely the equivalence of all (inertial) observers. This justifies the term in the title.

The wide range of applications of atomic interferometry and of laser interferometry in the search for quantum gravity induced effects is presented. These effects consists of the exploration of relativistic gravity theories, tests of the Einstein Equivalence principle, of searches for quantum gravity induced deviations of the ordinary dispersion relation and of the search for fundamental fluctuations.

This review article aims at presenting the theory of inflation. We first describe the background spacetime behavior during the slow-roll phase and analyze how inflation ends and the Universe reheats. Then, we present the theory of cosmological perturbations with special emphasis on their behavior during inflation. In particular, we discuss the quantum-mechanical nature of the fluctuations and show how the uncertainty principle fixes the amplitude of the perturbations. In a next step, we calculate the inflationary power spectra in the slow-roll approximation and compare these theoretical predictions to the recent high accuracy measurements of the Cosmic Microwave Background radiation (CMBR) anisotropy. We show how these data already constrain the underlying in.ationary high energy physics. Finally, we conclude with some speculations about the trans-Planckian problem, arguing that this issue could allow us to open a window on physical phenomena which have never been probed so far.

In these lectures I review, in as much pedagogical way as possible, various theoretical ideas and motivation for violation of CPT invariance in some models of Quantum Gravity, and discuss the relevant phenomenology. Since the subject is vast, I pay particular emphasis on the CPT Violating decoherence scenario for quantum gravity, due to space-time foam. In my opinion this seems to be the most likely scenario to be realised in Nature, should quantum gravity be responsible for the violation of this symmetry. In this context, I also discuss how the CPT Violating decoherence scenario can explain experimental “anomalies” in neutrino data, such as LSND results, in agreement with the rest of the presently available data, without enlarging the neutrino sector.

Our understanding of spacetime has undergone some major changes in the last hundred years. Before last century, spacetime was regarded as nothing more than a passive and static arena in which events took place. Early last century, Einstein's general relativity changed that viewpoint and promoted spacetime to an active and dynamical entity. Nowadays, many physicists also believe that spacetime, like all matter and energy, undergoes quantum fluctuations. Following John Wheeler, many of us think that space is composed of an everchanging arrangement of bubbles called spacetime foam, a.k.a. quantum foam. To understand the terminology, let us follow Wheeler and consider the following simplified analogy which he gave in a gravity conference at the University of North Carolina in 1957. Imagine yourself flying an airplane over an ocean. At high altitude the ocean appears smooth. But as you descend, it begins to show roughness. Close enough to the ocean surface, you see bubbles and foam. Analogously, spacetime appears smooth on a large scale, but on sufficiently small scales, it will appear rough and foamy, hence the term “spacetime foam.” Many physicists believe the foaminess is due to quantum fluctuations of spacetime, hence the alternative term “quantum foam.” If spacetime indeed undergoes quantum fluctuations, the fluctuations will show up when we measure a distance (or a time duration), in the form of uncertainties in the measurement. Conversely, if in any distance (or time duration) measurement, we cannot measure the distance (or time duration) precisely, we interpret this intrinsic limitation to spacetime measurements as resulting from fluctuations of spacetime itself.

Gamma ray bursts (GRBs) are short and intense pulses of γ-rays arriving from random directions in the sky. Several years ago Amelino-Camelia et al. [1] (see also [2]) pointed out that a comparison of time of arrival of photons at different energies from a GRB could be used to measure (or obtain a limit on) possible deviations from a constant speed of light at high photons energies. I review here our current understanding of GRBs and reconsider the possibility of performing these observations (see also Norris, Bonnell, Marani, & Scargle [3] for a review of the same topic). I begin (in Sect. 2) with a brief discussion of the motivation to consider an energy dependent variable speed of light. I turn (in Sect. 3) to a general discussion of the detectability of deviations from a constant speed of light via time-lag measurments. I derive constraints on the Energy range, the distance to the sources and the needed temporal resolution of the sources and the detectors. I then turn (in Sect. 4) to a short description of our current understanding of GRBs. This section is included as a background material as for the rest of the discussion GRBs are just cosmological sources of high energy photons and we don't really care how are these photons they produced. In Sect. 5 I return to the subject of the talk and I describe the temporal structure and spectral properties of GRBs. These are the key issues that are relevant for the observations of a variable speed of light. I conclude (in Sect. 6) by confronting the observations needed for determination of (or obtaining a limit on) a variable speed of light with the properties of GRBs. I discuss some recent attempts to obtain limits on Quantum Gravity effects [4, 5, 6, 7] and prospects for future improvements.